Novel approach to diet design for determining macronutrient preference.

Previous studies indicate that rats fed a saturated vs. unsaturated fat consume more of a high-protein/low-carbohydrate and less of a low-protein/high-carbohydrate diet. Present studies were conducted to determine whether saturated-fat-fed rats are preferring protein or avoiding carbohydrate. Three combinations of diets were prepared in which one macronutrient was held constant and two covaried: 1) high protein/low carbohydrate and low protein/high carbohydrate, 2) high fat/low carbohydrate and low fat/high carbohydrate, and 3) high fat/low protein and low fat/high protein. Male Sprague-Dawley rats (75-99 g) were fed either 34% tallow (n = 30) or corn oil (n = 30) diets for 4 days. These diets were removed and one third of each group was given one of the diet combinations. Rats previously fed tallow consumed more high-protein/low-carbohydrate and low-carbohydrate/high-fat diets and less high-carbohydrate/low-fat diet than controls previously fed corn oil. These data suggest that tallow-fed animals are avoiding carbohydrate rather than preferring protein.